1. Field of the Invention
The invention relates to a material of a cycloolefin copolymer for extruded and injection-molded articles and to a process for its preparation.
2. Description of Related Art
For the production of recording media, such as optical information carriers, for example optical disks or compact disks, various layers of nitrides, oxides and rare earth/transition metal alloys are usually sputtered onto a prestamped substrate of polycarbonate resin, polymethyl methacrylate, epoxy resin, polysulfone, polyether-sulfone or polyether-imide. The fidelity of reproduction of the information recorded and the long-term stability of the information carrier here depends greatly on the substrate material. For example, the dimensional stability under heat and the birefringence of the substrate material influence the fidelity of reproduction decisively, while the absorption of moisture by the plastics quite considerably influences the long-term stability of the physical properties of the recording layers.
The substrates are generally produced by the injection molding technique, wherein the groove or pit matrix is transferred to the substrates of plastic by means of an original (stamper). The faithfulness of this copy to the original depends very greatly on the processability of the injection-molded material. It is known that polymeric materials which have good flow properties under processing conditions also guarantee a good image quality.
EP-A 0 310 680 describes a recording medium (MOD) in the form of a magneto-optical storage disk with a substrate of an amorphous ethylene/tetracyclododecene copolymer, which carries a magneto-optical recording layer of a quaternary amorphous rare earth/transition metal alloy of Tb, Fe and Co, with Pt or Pd as further alloying components.
A magneto-optical recording layer of Te, Ge and Cr which is sputtered onto a substrate of an amorphous copolymer of ethylene with 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, abbreviated to DMON, is known from Example 4 of EP-A 0 387 016.
Other known substrate materials are polymer alloys of polycarbonate and polystyrene and cycloolefin copolymers, such as are described in U.S. Pat. No. 4,614,778 and in EP-A 0 387 018, column 5, lines 5 to 24.
The build-up of a storage disk (OD) for which the material according to the invention is suitable as a substrate is described in German Patent 41 37 427,=U.S. Ser. No. 07/974,856.
The rotating speeds of storage disks and, associated with these, storage densities which can be achieved without loss in quality of reproduction are limited by the mechanical properties of the substrate, in particular the modulus.
Cleaning, coating and gluing of the substrate materials is limited by the specific resistance of the particular substrate material to solvents.